1. Field of the Invention
The present invention relates to an optical disk drive for reading and/or writing data from/on an optical disk on which pre-pits, representing address information and other types of information, have been formed.
2. Description of the Related Art
Recently, recordable optical disks of various types, including CD-R and CD-RW, have been popularized as storage media for storing computer data or recording music thereon. In the meantime, new types of optical disks with a storage capacity high enough to store video data thereon, e.g., DVD-RAM, DVD-R and DVD-RW, have also been put on the market just lately. Among these new optical disks, the DVD-R and the DVD-RW have disk formats similar to that of a DVD-ROM as a read-only medium so as to be read by a read-only DVD drive relatively easily.
More specifically, as shown in FIG. 1, an optical disk 4 such as a DVD-R has grooves for guiding a light spot during a data read/write operation. Data is written on and along these grooves. These grooves are wobbled at a constant frequency to generate a reference clock signal for use to control the number of revolutions of the disk 4. Also, pre-pits have been formed on land(s) that is/are adjacent to each of those grooves. The xe2x80x9clandxe2x80x9d is a disk area between a pair of grooves. These pre-pits (i.e., so-called xe2x80x9cland pre-pitsxe2x80x9d) are used to correct the phase of a write clock signal during a data write operation, for example. By using these pre-pits that have been formed in advance on the optical disk, the write operation can be performed even more accurately.
Just like the wobble pattern of a groove, each pre-pit that has been formed on a land adjacent to a groove is detected as a differential signal representing a difference between the intensity of light that has been reflected from an outer land and that of light that has been reflected from an inner land. As used herein, the xe2x80x9couter landxe2x80x9d refers to a land that is adjacent to a groove in the radial direction of the disk and closer to the outer periphery of the disk, while the xe2x80x9cinner landxe2x80x9d refers to a land that is adjacent to the same groove in the radial direction of the disk and closer to the inner periphery of the disk. FIG. 2 illustrates a differential signal that has been detected in this manner and converted into an electric signal. As shown in FIG. 2, the differential signal includes a wobble signal component representing wobbling information and a pre-pit signal component corresponding to the pre-pits. A method for detecting the pre-pit signal component is described in Japanese Laid-Open Publication No. 2000-195058, for example.
However, the pre-pits to be formed on the disk are sometimes deformed and cannot take their desired shapes depending on the cutting conditions of the disk manufacturing process, for example. Also, a signal representing a pre-pit detected may have its amplitude varied because a read beam spot detected by an optical pickup is likely to have a deformed shape in the disk radial direction, in particular, and because the disk itself is sometimes warped or tilted. Furthermore, if data was already written on a recording track, a signal component representing the written data, which should have been eliminated from a differential signal, might be detected from the differential signal. For these reasons, the pre-pit signal may sometimes be detected inaccurately depending on a particular combination of the disk and the disk drive used.
Accordingly, in an optical disk drive, the circuit section thereof for detecting the pre-pit signal needs to be appropriately adjusted to the individual disk drive/disk combination. Recently, in particular, as the density of the data written on a disk goes on increasing, it becomes more and more difficult to detect the pre-pit signal accurately enough. Thus, an optical disk drive to deal with an optical disk having an even higher storage capacity must detect the pre-pit signal, and generate a sync signal, even more accurately.
In order to overcome the problems described above, an object of the present invention is to provide an optical disk drive that can detect the pre-pit signal even more accurately.
An optical disk drive according to the present invention is used to read and/or write data from/on an optical disk on which a pre-pit has been formed on at least one side edge of a data recording track. The disk drive includes light-emitting element, photodetector section, subtractor and amplifier. The light-emitting element emits a light beam and irradiates the track of the optical disk with the light beam. The photodetector section receives and detects the light beam that has been reflected from the track, thereby generating first and second detection signals based on the reflected light beam. The first and second detection signals carry information about a shape of the track at the one side edge thereof and information about a shape of the track at the other side edge thereof, respectively. The subtractor generates a differential signal representing a difference between the first and second detection signals. The amplifier amplifies the differential signal, which has been output from the subtractor, by a variable amplification factor and outputs an amplified differential signal. The optical disk drive detects the pre-pit in accordance with the amplified differential signal.
In one preferred embodiment of the present invention, the optical disk drive further includes a pre-pit detection decision circuit for determining whether or not a signal component of the amplified differential signal representing the pre-pit corresponds to the pre-pit that has been actually formed on the optical disk. The amplification factor is defined for the amplifier in accordance with the output of the pre-pit detection decision circuit.
In this particular preferred embodiment, the optical disk drive preferably further includes a digitizer for digitizing the amplified differential signal and outputting a digital signal representing the pre-pit. The pre-pit detection decision circuit determines whether or not the digital signal corresponds to the pre-pit that has been actually formed on the optical disk.
More particularly, the amplification factor of the amplifier is preferably defined while being changed with a slice level of the digitizer fixed.
In still another preferred embodiment, the amplification factor of the amplifier is defined in accordance with the differential signal representing the difference between the first and second detection signals that have been generated based on the light beam reflected from a part of the track on which no data has been written yet.
In yet another preferred embodiment, the light-emitting element records information representing the defined amplification factor on the optical disk.
In yet another preferred embodiment, the optical disk drive further includes a storage device for storing information representing the defined amplification factor thereon.
In yet another preferred embodiment, the optical disk drive further includes a balance controller for adjusting a balance between the first and second detection signals. The subtractor generates the differential signal representing the difference between the first and second detection signals that have had their balance adjusted.
In this particular preferred embodiment, the optical disk drive further includes a pre-pit detection decision circuit for determining whether or not a signal component of the amplified differential signal, representing the pre-pit, corresponds to the pre-pit that has been actually formed on the optical disk.
More particularly, the optical disk drive preferably further includes a pre-pit detection percentage calculator for calculating a pre-pit detection percentage based on a result obtained by the pre-pit detection decision circuit. The balance controller preferably defines the balance by the pre-pit detection percentage.
In that case, the optical disk drive preferably further includes a digitizer for digitizing the amplified differential signal and outputting a digital signal representing the pre-pit. The pre-pit detection decision circuit preferably determines whether or not the digital signal corresponds to the pre-pit that has been actually formed on the optical disk.
In such a preferred embodiment, the optical disk drive further includes a slice level changer for changing a slice level at the digitizer. The slice level changer preferably defines the slice level in accordance with the pre-pit detection percentage.
More specifically, when predetermined initial values of the balance and the slice level are represented by B0 and S0, respectively, the balance to be defined is preferably estimated by comparing an initial pre-pit detection percentage D (B0) corresponding to the initial balance value B0 with another pre-pit detection percentage D (B1) corresponding to another balance value B1, which is greater or smaller than the initial balance value B0 by a predetermined difference xcex94B, and the slice level to be defined is preferably estimated by comparing another initial pre-pit detection percentage D (S0) corresponding to the initial slice level S0 with another pre-pit detection percentage D (S1) corresponding to another slice level S1, which is greater or smaller than the initial slice level S0 by a predetermined difference xcex94S.
Alternatively, the balance and the slice level may be defined in accordance with the differential signal representing the difference between the first and second detection signals that have been generated based on the light beam reflected from a part of the track on which data has already been written.
As another alternative, the balance and the slice level may also be defined while data is being written on the track of the optical disk.
In yet another preferred embodiment, the light-emitting element records information representing the defined balance and information representing the defined slice level on the optical disk.
In yet another preferred embodiment, the optical disk drive further includes a storage device for storing the defined balance and the defined slice level thereon.
In yet another preferred embodiment, the track of the optical disk has a wobble pattern. The optical disk drive further includes a wobble digitizer for generating a digital signal representing the wobble pattern. And responsive to a pre-pit predicted signal that has been generated in accordance with the output of the wobble digitizer, the pre-pit detection decision circuit determines whether or not the signal component of the differential signal representing the pre-pit corresponds to the pre-pit that has been actually formed on the optical disk.
Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.